The Blood War is in simplest terms the eternal war between the two major denizen of the lower planes. The Baatezu, from Baator, and the Tanar'ri, from the Abyss, are the two main factions in the war. The Baatezu are the representatives of vicious law and cruel order in the conflict while the Tanar'ri are the forces of chaos in its purest form. Both of the forces have an inborn hatred of one another, no sage has ever figured out why or what would happen if you separated one from his race, but that's the way the war is.

The Blood War is all consuming and most think that it's a never-changing, futile stalemate; but each side has come very close to defeating the other on many occasions. Every inch of the planes, at one time or another, has had blood spilled on it from this conflict. Even the mighty Archons and Solars wield little power in the war. The thing that many berks don't realize is that no matter who you are, it don't matter in the grand theme of things. No matter how many Pit Fiends or Balors you kill, you ain't going to change much.

Why doesn't the forces of good try to stop them or swing the balance? Well the answer isn't a simple one. First of all, it is the very nature of good to stop evil, not smite it. Doing such an atrocious act as killing billions of Lemures (the "cannon fodder" of the Baatezu) is still killing in any light. Likewise, remember there is still a division line in the forces of good, law and chaos. No matter how hard you try you can't get anyone to agree to one another. The Archons wanna destroy the Tanar'ri while the Aasimon wanna take out the Baatezu. You can't get them to agree on anything. Second, if you help eradicate the forces of chaos and evil, the Tanar'ri, the Baatezu are going to turn their attention toward something else; like the Modrons or the Slaadi. In the end you are stuck with someone always being at war. What hope would the Lady of Pain have trying to keep out the entire race of Baatezu or even the mighty Mediators of Mechanus? In reality very little. Both of these races have been warring since the beginning of time and have perfected their races for war against any foe. It's easier just to make sure they keep fighting each other.

The thing about the Blood War is that it is all consuming. It has bent EVERYTHING in its path. The noble Archons have even resorted to supplying one side or another with weapons. The Blood War creates a great need for supplies, weapons, troops and leaders. Many bashers capitalize on these needs to earn some jink of their own. Some "brave" planewalkers deal in weapons or mercenaries with either or both sides. The Yugoloths, natives of the Gray Waste and Gehenna, devote a great deal of time and energy in helping both sides --but only so they can earn a fair profit.

People said that the tale of war is written by the victors so you ain't ever gonna get an accurate retelling of the war. That's the one role that the Yugoloths fill that may be of usefulness. The Arcaenoloths sit next to their furnaces on Gehenna and write what really happens during the Blood War. The only problem is no basher's ever been able to bring back a Yugoloth text from Gehenna alive.